Polyisocyanurate compositions and foams of improved friability and process of preparing same

ABSTRACT

In a process of preparing a polyisocyanurate foam, which process comprises: reacting a polyisocyanate in the presence of a trimerization catalyst and an expanding amount of an inert blowing agent to provide a polyisocyanurate foam, the improvement which comprises: carrying out the reaction in the presence of a plasticizing amount of a nonvolatile liquid carbonate to produce a polyisocyanurate foam having improved friability and dimensional stability properties.

BACKGROUND OF THE INVENTION

Polyisocyanates, such as aliphatic and aromatic isocyanates likediisocyanates, have been polymerized in the presence of a trimerizationcatalyst to provide rigid polyisocyanurate foams. The polyisocyanatetrimerization reaction has been carried out in bulk and in solution toprovide essentially cross-linked, very brittle and very friable foamproducts. The foam products are produced by combining polyisocyanate, aninert blowing agent, such as a low-boiling-point liquid likehalocarbons, and one or more trimer catalysts like a tertiary amine, andmixing to effect the polyisocyanurate reaction. Typically, the reactionis exothermic on mixing the components, and no additional heating isrequired. The polyisocyanurate foams produced to date have not beencommercially acceptable, and have been characterized by high brittlenessand friability. Brittleness refers to the internal friability of thefoam structure which remains essentially unchanged with time; that is,it is structural and molecular in nature, while friability refers to thestate of the surface of the polyisocyanurate foam; that is, thepowderability of the surface when subject to pressure, which friabilitychanges with time.

Attempts to reduce the friability of polyisocyanurates have been made bymodification of the polyisocyanurate principally through theintroduction of other chemical linkages. Epoxy-modified isocyanurateshave not been commercially acceptable, since they are expensive, thereaction is difficult to control and the materials exhibit limitedprocessing properties. Imide-modified isocyanurates are very thermallystable with high thermal conductivity, but also are prepared fromexpensive raw materials. Carbodiimide-modified isocyanurates also areexpensive and the reaction is difficult to control. The present-day,best, commercial products are the urethane-modified isocyanurateproducts which, although expensive, can be prepared by known and readilyavailable commercial catalytic agents, and provide foams of relativelygood thermal and flame-resistant properties.

In the preparation of such polyisocyanurate; i.e., trimer, foamsconsisting essentially of recurring cross-linked isocyanurate units andthe modified polyisocyanurates, a wide variety of trimer catalysts andcombinations have been suggested and used (see, for example, U.S. Pat.Nos. 3,487,080; 3,723,364; 3,736,298; and 3,759,916). Such trimercatalysts have included tertiary amines, such as N,N'-dialkylaminoalkylphenols and the like.

The base trimerization of isocyanates in the presence of ethylenecarbonate has been reported to result in the acceleration of thetrimerization process and in the formation of a solid complex of thepolyisocyanurate-ethylene carbonate (see Tsuzuki et al, "New Reactionsof Organic Isocyanates. I. Reaction with Alkylene Carbonates," Journalof Organic Chemistry, Vol. 25, 1009, June 1960). Further, the reactionof propylene carbonates with polyisocyanurates is set forth in Saundersand Frisch, "Polyurethanes: Chemistry and Technology," High Polymers,Vol. XVI, Part 1, page 116, Interscience Publishing Co., Inc. Organiccarbonates have also been used as modifiers in noncellular urethaneresins (see U.S. Pat. No. 3,883,466).

It is, therefore, most desirable to provide trimer isocyanurate foams,both modified and unmodified, which have low friability while retainingthe other desirable properties of such foams, and methods of preparingsuch foams which provide for improved and rapid process conditions andcure of the polyisocyanurate foams.

SUMMARY OF THE INVENTION

Our invention relates to polyisocyanurate foams of enhanced friabilityand to the process of preparing such foams. In particular, our inventionconcerns organic carbonate-polyisocyanurate foamable compositions andfoams and the process of employing organic carbonate, such as alkylenecarbonates, in the preparation of such compositions and foams.

Our invention comprises a polyisocyanurate foam which includes aplasticizing nonreactive amount of an organic carbonate therein toprovide for a unique and unexpected reduction in the friability of thefoam, both for modified and unmodified foams, but particularly as tounmodified polyisocyanurate foams; that is, foams consisting essentiallyof the isocyanate trimer with recurring isocyanurate linkages. We havefound that the preparation of polyisocyanurate foams in the presence oforganic cyclic carbonates and liquid alkylene carbonates like ethylene,propylene and butylene carbonates, in the preferred embodiments, andmixtures thereof, in amounts of, for example, from about 0.5 50% byweight of the composition, considerably and unexpectedly reduces thefriability of the resulting foams. More particularly, we have discoveredthat low concentrations of generally from about 0.5 to 10% by weightconsiderably reduces the friability of unmodified or trimerpolyisocyanurate foams, while, at higher concentration levels; forexample, from about 25 to 50% by weight, the trimer foam products areenhanced in foam qualities approaching that or equal to the knownpolyisocyanurate modified foams, and approximately equivalent to thepresent normal polyurethane foam performances. The organic carbonatesuseful in our ivnention include, but are not limited to, thosehigh-boiling-point nonvolatile cyclic and acyclic carbonates set forthin U.S. Pat. No. 3,883,466, herein incorporated by reference.

In contrast to the use of other nonreactive organic plasticizers, ourorganic carbonates, particularly at the preferred level, do notsignificantly alter the flammability characteristics of the foamedproduct as measured by commonly applied laboratory test methods. Othernonreactive plasticizer additives, such as organic plasticizers,significantly increase the flammability of the polyisocyanate foam atthe high level of usage required to produce an acceptable nonfriablefoam product with such plasticizers.

We have found that, by infrared analysis of our polyisocyanurate foamswith the use of propylene carbonate, the propylene carbonate is presentin the foam without chemical change; i.e., in its original structure.The effectiveness and advantage of liquid alkylene carbonate in theproduction of our polyisocyanurate foams over more commonly usedplasticizers have been demonstrated in a number of experiments.

A wide variety of organic carbonates may be employed to reducefriability and to obtain the benefits of our invention; for example,particularly the liquid C₂ -C₆ cyclic alkylene carbonates, such aspropylene carbonate. Due to cost and ready availability, propylenecarbonate is preferred.

We have found that the preferred alkylene carbonate provides for apolyisocyanurate foam of low density which has little initialfriability, foam brittleness or shrinkage, all of which properties havebeen characteristics of previously unmodified trimer polyisocyanuratefoams. Our polyisocyanurate foamable composition is a two-component,one-shot, foamable composition, which, on mixing the component parts,provides for the reaction of the components into a polyisocyanurate foamproduct, either by its own heat exotherm or reaction, or, if desired, bythe addition of external heat. One component may comprise an isocyanatecompound, either aliphatic or aromatic, which term also includesisocyanate-terminated urethane prepolymers, as well as polyol and otherwell-known modified polyisocyanurate prepolymers.

The isocyanate is subject to trimerization to a polyisocyanurate in thepresence of a trimer catalyst. In particular, the preferred catalystsystem is a combination of a major amount of a dialkylaminoalkyl phenol,such as dimethylaminomethyl phenol, and a minor amount of triethylenediamine in a cocatalyst system as set forth in the copending U.S. patentapplication of Henry S. Hopkins, Jr., U.S. Ser. No. 596,367, filed July16, 1975, entitled POLYISOCYANURATE FOAMS PREPARED BY A COCATALYSTSYSTEM.

The second component of the composition comprises a trimerizationcatalyst system, such as a tertiary amine metal salt or other trimercatalyst, either alone or in combination, and typically in an amount offrom about 0.5 to 15% by weight. In addition, the second componentincludes an expanding amount of an inert blowing agent, typically aliquid compound, such as a hydrocarbon or halocarbon, which volatilizesduring the trimerization exothermic reaction to produce the cellular orfoam structure, or a chemical blowing agent which decomposes by anin-situ generation of an inert gas. Typical blowing agents include, forexample, a fluorine-containing lower alkene, such as difluoro dichloromethane or trichloro monofluoro methane and other well-known agents. Thesecond component may also include a surfactant or cell-control agent,such as a silicone product or a silicone glycol ether product, to aid inthe preparation of the foam and to control cell size. Other additives ofthe second component may include plasticizers, such as nonvolatileliquid esters, hydrocarbons, phosphates and the like, and otheradditives or modifying agents, such as flame and smoke-retardantadditives, stabilizers, synergists, polyols, resins, fillers and thelike.

A wide variety of organic isocyanates may be employed which are subjectto trimerization which includes, but is not limited to: methylene bisphenyl isocyanate and its isomers and mixtures thereof; polymethylenepolyphenyl polyisocyanate; meta or para phenylene diisocyanate;hexamethylene diisocyanate; toluene diisocyanate; diphenylmethanediisocyanate and the like. The alkylene carbonates may be added toeither or both components or added directly after mixing the twocomponents. The process is carried out by simply mixing the components,with the reaction occurring in the presence of the catalyst system atroom temperature (60°-80° F.) by virtue of the reaction exotherm.

Our invention will be described and set forth for the purpose ofillustration only in connection with the following examples; however, itis recognized and is part of our invention that various substitutionsand modifications can be made in the formulations and techniques withoutdeparting from the spirit and scope of our invention.

DESCRIPTION OF THE EMBODIMENTS

A master formulation (Parts A and B) was prepared and the parts mixed toprovide a polyisocyanurate foam with the amount of plasticizer remainingconstant, but wherein the plasticizer compound was changed. Theremitting foam was then visually examined and tested for friability anda ball drop test was carried out on the cured foam.

                  TABLE I                                                         ______________________________________                                        Master Formulation                                                                                      Parts                                               Part A                    by Weight                                           ______________________________________                                        Mondur MR (a crude polymeric isocyanate                                       of polymethylene polyphenyl diisocyanate                                      from Mobay Chemical Co.) - various isocy-                                     anates can be used with NCO/OH > -5000                                                                  66.66                                               Part B                                                                        1.    Amine cocatalyst system                                                        dimethylaminomethyl phenol                                                                           5.43                                                   triethylene diamine    0.77                                            2.    Surfactant cell-control agent -                                               DC-193                                                                         silicone-glycol copolymer of Dow                                              Corning Co.            2.33                                            3.    Blowing agent                                                                  fluorotrichloromethane 17.06                                           4.    Plasticizer             7.75                                                                          100.00                                          ______________________________________                                    

                  TABLE II                                                        ______________________________________                                        Formulation No.                                                                          Plasticizer     Result                                             ______________________________________                                        1          Butyl cellosolve                                                                              Very friable                                       2          Phosgard C-22R.sup.1                                                                          Extreme friability                                            (chlorinated phos-                                                            phate ester)                                                       3          Firemaster T-23P.sup.2                                                                        Extreme friability                                            (tris (2,3-dibromo                                                            propyl phosphate)                                                  4          Cellosolve acetate                                                                            Moderate friability                                5          Fyrol CEF.sup.3 Moderate friability                                           (tris (2-chloro-                                                              ethyl phosphate)                                                   6          Antiblaze 78.sup.4                                                                            No foam rise                                                  (chlorinated phos-                                                            phate)                                                             7          Dioctylphthalate                                                                              Very friable                                       8          Propylene carbonate                                                                           No friability                                      9          Wingstay T.sup.5                                                                              Very friable                                                  (hindered phenol)                                                  ______________________________________                                         .sup.1 a trademark of Monsanto Chemical                                       .sup.2 a trademark of Michigan Chemical                                       .sup.3 a trademark of Stauffer Chemical                                       .sup.4 a trademark of Mobile Oil                                              .sup.5 a trademark of Goodyear Chemical                                  

Ball-drop testing of the cured foams from above confirms the presence ofmore brittle polymer formation, except for propylene carbonateformulation No. 8. All of the foams are "powdered" in the impactindentation area.

In addition, heat-aging of the foam products shows that the propylenecarbonate provides also for improved dimensional stability of the foam.

                  TABLE III                                                       ______________________________________                                        Dry heat-aging of the above formula for 4 hours at 200° F.:            ______________________________________                                        No. 1                                                                              Moderate Shrinkage                                                                           No. 6  Moderate Shrinkage                                 No. 2                                                                              Moderate Shrinkage                                                                           No. 7  Moderate Shrinkage                                 No. 3                                                                              Moderate Shrinkage                                                                           No. 8  No Observable Dimension                                                        Change                                            No. 4                                                                              Severe Shrinkage                                                                             No. 9  Moderate Shrinkage                                 No. 5                                                                              Moderate Shrinkage                                                       ______________________________________                                    

Further experiments using the same master formula of Table I, but withan increase in the dimethylaminomethyl phenol catalyst to 12% in anattempt to cure more completely the polymer, did not significantly alterthe test results. An increase in the foam density from 2.0 pcf to 3.0pcf also produced similar results. Other variables, such as NCO/OHratio, cell size and reaction speeds (all within the constraint ofproducing adequate foams), did not significantly alter the test results.

Comparison testing of propylene carbonate indicates that concentrationlevels follow the results of other plasticizers, with the notableexception of the minimum level necessary for use. Most plasticizersbecome effective in reducing (or eliminating) friability at 15-30% byweight, whereas propylene carbonate gives an equivalent performance atlevels of 4-10% by weight. The obvious advantage of lower level use iseconomic; however, a lower level also gives a better foam product fromthe standpoint of physical properties.

Dry heat-aging at 400° F. for 4 weeks discolors and embrittles propylenecarbonate-containing foams; however, no other plasticizer tested at anyconcentration level survives even short time periods at 400° F. (1 dayor longer). Dry aging at 300°-350° F. indicates no significantdimensional change for alkylene carbonate-containing trimers, whileother plasticizer-containing trimers are discolored, further embrittledand have severe dimensional change.

Thus, we have discovered that organic carbonates can significantlyimprove the friability and dimensional stability of polysiocyanuratefoams.

What we claim is:
 1. In a process of preparing a polyisocyanurate foam,which process comprises: reacting a polyisocyanate in the presence of atrimerization catalyst and an expanding amount of an inert blowing agentin a foamable composition to provide a polyisocyanurate foam, theimprovement which comprises:carrying out the reaction in the presence ofa plasticizing amount of a nonreactive liquid organic carbonate, therebyproducing a polyisocyanurate foam having improved friability anddimensional stability properties.
 2. The process of claim 1 wherein thecarbonate comprises from about 0.5 to 50% by weight of the composition.3. The process of claim 1 wherein the carbonate is a C₂ -C₆ cycliccarbonate.
 4. The process of claim 1 wherein the carbonate is propylenecarbonate in an amount of from about 4 to 10% by weight of thecomposition.
 5. The process of claim 1 wherein the trimerizationcatalyst is a cocatalyst which comprises a dialkylaminoalkyl phenol anda triethylene diamine.
 6. The process of claim 5 wherein thedialkylaminoalkyl phenol is dimethylaminomethyl phenol.
 7. The processof claim 1 wherein the blowing agent is an inert fluorine-containinglower alkene liquid or hydrocarbon liquid which volatilizes during theexothermic catalytic reaction to produce the polyisocyanurate foam. 8.The process of claim 1 wherein the reaction composition includes asilicone surfactant as a cell-control agent.
 9. The process of claim 1wherein the polyisocyanate is an organic diisocyanate.
 10. The processof claim 1 wherein the polyisocyanate is a diisocyanate and the reactionconsists essentially of the diisocyanate to produce an unmodified trimerpolyisocyanurate foam.
 11. The process of claim 1 wherein thepolyisocyanate is an isocyanate-terminated urethane prepolymer.
 12. In aprocess of preparing a polyisocyanurate foam consisting essentially ofrecurring isocyanurate linkages, which process comprises: reacting anorganic diisocyanate, in the presence of a dialkylaminoalkyl phenol anda tris ethylene diamine as a cocatalyst and in the presence of a blowingamount of an inert blowing agent which volatilizes during the exothermiccatalytic reaction, in a foamable composition to provide apolyisocyanurate foam of improved friability and dimensional stability,the improvement which comprises:carrying out the reaction in thepresence of from about 1 to 10% by weight of the composition ofnonreactive propylene carbonate to provide a polyisocyanurate foam ofimproved friability and dimensional stability.
 13. A polyisocyanuratefoam which comprises a cured, cellular, polyisocyanurate foam whichcontains a plasticizing amount of a nonreacted liquid organic carbonatetherein, the foam characterized by improved friability and substantiallyno observable shrinkage on heat-aging at temperatures up to 200° F. fortimes up to 4 hours.
 14. The foam of claim 13 wherein the carbonatecomprises from about 0.5 to 50% by weight of the foamable compositionfrom which the foam is prepared.
 15. The foam of claim 13 wherein thecarbonate is propylene carbonate.
 16. The foam of claim 13 wherein thecarbonate is propylene carbonate in an amount of from about 4 to 10% byweight of the foamable composition from which the foam is prepared. 17.The foam of claim 13 wherein the polyisocyanurate foam consistsessentially of recurring isocyanurate linkages.
 18. The foam of claim 13wherein the foam is derived from the reaction of an organic diisocyanatein the presence of a trimerization catalyst which comprises adialkylaminoalkyl phenol and a triethylene diamine.
 19. The foam ofclaim 13 wherein the polyisocyanate foam is derived from a polyethylenepolyphenol diisocyanate.